Method of improving the corrosion resistance of a metal

Abstract

A composite member includes a structural member having a surface in a mirror-finished condition and a film layer of an amorphous material provided on the surface. The amorphous material is preferably at least one selected from amorphous SiC, amorphous SiN, amorphous SiGe and amorphous GeN. In producing the composite member, a surface of a structural member is polished into a mirror-finished condition which is a finish condition by the usual mirror-finishing. The film layer of the amorphous material is then provided on the surface in the mirror-finished condition by plasma CVD process.

We claim: 
     
       1. A method for improving the corrosion resistance of a metal member, comprising the steps of: working a surface of the metal member to a surface condition such that the number of defects more than 1 μm in size existing in a circular area of a radius of 100 μm in any portion of said surface is no more than one; and   forming a film layer on said surface by plasma CVD process, said film layer comprising at least one material selected from the group consisting of amorphous SiC, amorphous SiN, amorphous SiGe and amorphous GeN.   
     
     
       2. The method of claim 1, wherein inner surfaces of a vessel constructed as a cathode are finished in said surface condition and plasma is produced all over said inner surfaces. 
     
     
       3. The method of claim 1, wherein metal members are arranged on an anode and a cathode, respectively, in a vessel filled with a raw material gas, and radio frequency power is applied to the raw material gas in the vessel to produce plasma. 
     
     
       4. The method for of claim 1, wherein said metal member is arranged on the side of a cathode in forming said film layer by the plasma CVD process. 
     
     
       5. The method of claim 1, wherein negative voltage is applied to said metal member in forming said film layer by the plasma CVD process. 
     
     
       6. The method for of claim 1, wherein said circular area has a radius of 400 μm worked surface is at the most one. 
     
     
       7. The method of claim 1, wherein said circular area has a radius of 200 μm.